1. Technical Field
This invention relates to an electronic device that includes a switching element and a drive circuit.
2. Related Art
There is known as an electronic device including a switching element and a drive circuit a power converter as disclosed in Japanese Patent No. 3430878.
The disclosed power converter includes an insulated gate bipolar transistor (IGBT), three metal-oxide-semiconductor field-effect transistors (MOSFETs), and a control circuit. A source terminal, a drain terminal, a gate terminal of a first MOSFET are electrically connected to a power supply for the drive circuit, a gate terminal of the IGBT, and the control circuit, respectively. A source terminal, a drain terminal, and a gate terminal of each of second and third MOSFETs are electrically connected to an emitter terminal of the IGBT, a gate terminal of the IGBT, and the control circuit, respectively.
The control circuit controls the three MOSFETs on the basis of a drive signal inputted from the external to drive the IGBT. When the drive signal instructs the control circuit to turn on the IGBT, the control circuit turns on the first MOSFET and turns off the second MOSFET, thereby charging the gate of the IGBT through the power supply for the drive circuit. Accordingly, a voltage on the gate (referred to as a gate voltage in the following) is increased higher than a turn-on/off threshold for turning on and off the IGBT, which leads to turn-on of the IGBT.
On the other hand, when the drive signal instructs the control circuit to turn off the IGBT, the control circuit turns off the first MOSFET and turns on the second MOSFET, thereby discharging the gate of the IGBT. Accordingly, the gate voltage is decreased lower than the turn-on/off threshold, which leads to turn-off of the IGBT. When the gate voltage is further decreased lower than a predetermined value, the control circuit turns on the third MOSFET. This leads to further discharge from the gate of the IGBT, which allows the IGBT to be kept in an off-state.
In the above disclosed power converter, in the presence of a fault in the IGBT and/or MOSFETs, it is likely that an abnormal state will occur such that the control circuit is unable to turn off the IGBT in spite of the drive signal instructing the control circuit to turn off the IGBT. This is because the gate voltage doesn't become lower than the turn-on/off threshold due to the fault. Continuation of such an abnormal state may lead to heat generation in the IGBT, which in turn may lead to thermal destruction of the device.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing an electronic device that is capable of detecting an abnormal state such that a switching element is unable to be turned off in spite of a drive signal instructing turn-off of the switching element.